It is now well known that the comfort of a shoe depends not only on its correct anatomical fit but also on correct outward permeation of the water vapor that has formed inside the shoe due to perspiration.
However, this permeation of the water vapor must not compromise the waterproofness of the shoe.
Traditionally, breathable shoes are shoes that use natural materials such as leather or equivalent products, which however, in the presence of rain or bad weather, indeed because of their permeation properties, do not ensure good waterproofness and indeed absorb water rather easily.
For this reason, shoes with an upper made of leather (or the like) coupled with a lining provided with a breathable and waterproof membrane (for example made of a material such as Gore-Tex® or the like), sewn or glued to an insole, have now been in use for a few years.
In the manufacture of these shoes, it is critical to pay attention to the seal of the regions where the insole and the lining connect to the membrane and the sole, in order to avoid even the slightest seepage of water from outside.
Most of the perspiration of the foot is generated at the interface between the sole of the foot and the sole of the shoe, which is typically made of polymeric material; it is evident that the perspiration that has formed on this interface is unable to evaporate, consequently condensing on the plantar insert on which the foot rests. Only a small percentage of the perspiration evaporates through the upper.
Accordingly, shoes that have breathable and waterproof soles have now been studied for years.
One of these soles is disclosed in U.S. Pat. No. 5,044,096 and in EP-0382904, and consists in dividing the sole, made of plastic material, into two layers with through holes and in interposing a membrane that is impermeable to water and breathable (made for example of a material such as Gore-Tex® or the like) and is joined perimetrically and hermetically to the two layers, so as to hinder any water infiltrations.
This sole ensures correct vapor permeation as well as an effective exchange of heat and water vapor between the environment inside the shoe and the external environment, at the same time ensuring the necessary waterproofness with respect to external humidity and water.
To provide a completely waterproof shoe, it is possible to couple a waterproof breathable sole to a waterproof breathable upper such as those described.
The step of waterproofing the regions connecting the insole and the lining to the membrane is also critical in the manufacture of shoes of this type.